Despite prompts from the field of family therapy since its inception, contemporary infant mental health theory and practice remain firmly rooted in and guided by dyadic-based models. Over the past 10 years, a groundswell of new empirical studies of triadic and family group dynamics during infancy have substantiated that which family theory has contended for decades: looking beyond mother-infant or father-infant dyads reveals a myriad of critically important socialization influences and dynamics that are missed altogether when relying on informant reports or dyad-based interactions. Such family-level dynamics emerge within months after infants are born, show coherence through time, and influence the social and emotional adjustment of children as early as the toddler and preschool years. This report summarizes key findings from the past decade of empirical family studies, highlights several areas in need of further conceptual development and empirical study by those who work with infants and their families, and outlines important implications of this body of work for all practicing infant mental health professionals.